1. Field of the Invention
The present invention relates to an ontology-integration-position specifying apparatus, an ontology-integration supporting method, and a computer program product that support association between classes included in an integration-source ontology and classes included in an integration-destination ontology.
2. Description of the Related Art
In recent years, the ontology in which knowledge or a concept is systematically classified and described has been used in many industries. In a general ontology, knowledge or a concept is expressed as a class hierarchy in which an attribute (property) of a superclass is inherited by a subclass. Superclass-subclass relationships are transitive. For example, when class A is a superclass of class B, and class B is a superclass of class C, class A is a superclass of class C. On the other way around, when class C is a subclass of class B, and class B is a subclass of class A, class C is a subclass of class A. Each class in the class hierarchy is associated with data (or a group of data pieces) which is described according to the attribute of the pertinent class. The associated data (or the group of data pieces) is called an “instance” of the class or the class hierarchy.
One distinguished characteristic of the class hierarchy is that the instances held by the subclasses can be viewed from the superclasses. This is because the subclass inherits the attribute of the superclass. Further, when the instance held by the subclass is viewed from the superclass, only values corresponding to the attributes held by the superclass can be viewed.
One technique that systematically represents vocabularies and knowledge present on a web and relations therebetween is the Web Ontology Language (OWL). The OWL, which is recommended by the World Wide Web Consortium (W3C), is designed to express a classification system of deducible vocabularies based on a collection of Subject, Predicate, and Object triplets of Resource Description Framework (RDF). An ontology is also used as a data model in various areas in industries, for example, in the PLIB (ISO 13584/Parts Library), which provides an international standard for industrial data.
When the concept and the instances thereof are managed by the ontology, a plurality of ontologies sometimes needs to be integrated. For example, when a merger of a companies or unification and reorganization of departments occurs, the ontologies managed in each company or each department need to be integrated and the instances need to be managed in an integrated manner.
In some cases, it may be desirable to reuse one of the existing ontologies, rather than constructing a brand-new ontology. When one existing ontology (hereinafter also referred to as integration-destination ontology) is to be reused, classes of the other existing ontology (hereinafter also referred to as integration-source ontology) may be added to the class hierarchy of the reused, existing ontology, or the existing class hierarchy may be expanded, so that the classes are properly allocated. Thus, the instances stored in the integration-source ontology can be integrated into the integration-destination ontology and managed by the integration-destination ontology.
As a technique for integrating the ontologies, various techniques have been proposed. For example, a technique described in JP-A 2001-14166 (KOKAI) is intended to compare and analyze attributes of classes of respective ontologies, find similarity between the classes, and associates the classes with each other when the classes that belong to different ontologies have a high degree of similarity. Such a technique facilitates the integration of ontologies by clarifying the correspondence between the classes in the ontologies.
The technique disclosed in JP-A 2001-14166 (KOKAI), however, does not take into consideration the granularity of the attributes held by the classes of the integration-source ontology and the integration-destination ontology. When the corresponding classes of the two ontologies have attributes with different granularities, the association of the classes and the attributes cannot be performed properly.
The granularity of the attribute is a measure of a scope encompassed by the attribute. For example, if a generic attribute “height” of the integration-source ontology is associated with a specific attribute such as “height in lying position” or “height in upright position” of the integration-destination ontology, there is a certain difference in the scopes encompassed by the respective attributes.
When the attribute of a class included in the integration-source ontology and the attribute of a class included in the integration-destination ontology are different in granularity, one attribute of one ontology comes to be associated with plural attributes of the other ontology. When two ontologies have many attributes with different granularities, a significantly large number of attributes of one ontology end up being associated with one attribute of the other ontology. When an attribute of one ontology can be associated with plural attributes of the other ontology, it is difficult to automatically choose one proper, corresponding attribute. Then, the automatic determination of a corresponding attribute is obstructed.